Antioxidant Capacity of Free and Bound Phenolics from Olive Leaves: In Vitro and In Vivo Responses.

Olive leaves are rich in phenolic compounds. This study explored the chemical profiles and contents of free phenolics (FPs) and bound phenolics (BPs) in olive leaves, and further investigated and compared the antioxidant properties of FPs and BPs using chemical assays, cellular antioxidant evaluation systems, and in vivo mouse models. The results showed that FPs and BPs have different phenolic profiles; 24 free and 14 bound phenolics were identified in FPs and BPs, respectively. Higher levels of phenolic acid (i.e., sinapinic acid, 4-coumaric acid, ferulic acid, and caffeic acid) and hydroxytyrosol were detected in the BPs, while flavonoids, triterpenoid acids, and iridoids were more concentrated in the free form. FPs showed a significantly higher total flavonoid content (TFC), total phenolic content (TPC), and chemical antioxidant properties than those of BPs (p < 0.05). Within the range of doses (20-250 µg/mL), both FPs and BPs protected HepG2 cells from H2O2-induced oxidative stress injury, and there was no significant difference in cellular antioxidant activity between FPs and BPs. The in vivo experiments suggested that FP and BP treatment inhibited malondialdehyde (MDA) levels in a D-galactose-induced oxidation model in mice, and significantly increased antioxidant enzyme activity of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and the total antioxidant capacity (T-AOC). Mechanistically, FPs and BPs exert their antioxidant activity in distinct ways; FPs ameliorated D-galactose-induced oxidative stress injury partly via the activation of nuclear factor erythroid-2-related factor 2 (Nrf2) signaling pathway, while the BP mechanisms need further study.

Dynamics of the glucosinolate-myrosinase system in tuber mustard (Brassica juncea var. tumida) during pickling and its relationship with bacterial communities and fermentation characteristics.

Pickled tuber mustard is a traditional fermented pickle widely consumed in China, and it is characterized by the presence of glucosinolates (GSLs). To understand the biotransformation of GSLs in tuber mustard during pickling, the dynamics of the glucosinolate-myrosinase (GSL-MYR) system and its potential associations with bacterial communities and fermentation characteristics (i.e., salinity, titratable acidity [TAA], and pH) were investigated. In total, 18 GSLs were identified in fresh tuber mustard; 12 were aliphatic, 4 were indolic, and 2 were aromatic, with aliphatic sinigrin and aromatic gluconasturtiin being the dominating components. The pickling process resulted in complete degradation of GSLs, with isothiocyanates (ITCs) and nitriles being the main breakdown products. Total ITCs reached maximum concentrations on day 21-28, while total nitriles peaked at the end of pickling. Based on Spearman's correlation analysis, our study showed that lactic acid bacteria (LAB) species might contribute to GSL transformation in pickled tuber mustard. Specifically, Weissella paramesenteroides, Pediococcus pentosaceus, and unclassified Lactococcus exhibited positive correlations with GSL contents (p < 0.01), suggesting that they might contribute to the increasing amounts of GSLs in the initial pickling, while the Lactobacillus-related populations that dominated in the later stages (i.e., Companilactobacillus alimentarius and Lactiplantibacillus Plantarum) were positively correlated with nitrile product concentrations. Moreover, redundancy analysis showed that pH and TAA had strong effect on myrosinase activity during tuber mustard pickling, which was dictated via the organic acids produced by microorganisms. This study provided a perspective for understanding the effect of fermentation on the transformation of tuber mustard GSLs.

Changes in Phytochemical Profiles and Biological Activity of Olive Leaves Treated by Two Drying Methods.

Olive leaves, which are the most abundant byproducts of the olive industry, offer multiple health benefits. The investigation of the phytochemical profiles and relevant biological activities is an essential step toward transforming these low-value byproducts into value-added ones. This study systematically investigated the phytochemical profiles, antioxidant capacity, and inhibition rates of olive leaves from four cultivars on the α-glucosidase, α-amylase, and angiotensin-converting enzyme (ACE). The leaves were prepared using two common drying methods, namely, hot air-drying and freeze-drying. A total of 33 bioactive compounds were identified in the olive leaves, namely, 19 flavonoids, 2 phenylethanoids, 2 coumarins, 2 hydroxycinnamic acids, 2 iridoids, and 6 triterpenic acids. Quantification of the bioactive compounds revealed high amounts of polyphenols, especially flavonoids [2,027-8,055 mg/kg dry weight (DW)], iridoids (566-22,096 mg/kg DW), and triterpenic acids (13,824-19,056 mg/kg DW) in the olive leaves. The hot air-dried leaves showed significantly (P < 0.05) higher iridoid (oleuropein and secoxyloganin) content than the fresh leaves, while freeze-drying resulted in significantly (P < 0.05) higher flavonoid aglycone and hydroxytyrosol content. Additionally, freeze-drying led to samples with the highest radical scavenging, α-amylase, α-glucosidase, and ACE inhibition abilities. The flavonoid (e.g., quercetin, luteolin, eriodictyol, kaempferol-7-O-glucoside, and luteolin-7-O-glucoside), hydroxytyrosol, and oleanolic acid contents in the olive leaves were positively correlated (P < 0.05) with their bioactive potentials.

The relationship of oxygen uptake rate and k(L)a with rheological properties in high cell density cultivation of docosahexaenoic acid by Schizochytrium sp. S31.

Three independent cultures by fed batch strategy under different oxygen supply levels were investigated with Schizochytrium sp. S31 on glycerol in 50 L bioreactor. Three cultures all achieved high cell density cultivation (HCDC) with more than 100 g/L biomass density. However, the culture with middle oxygen supply level achieved the highest DHA concentration at 21.26 g/L. Dissolved oxygen (DO) limitation was commonly encountered in the present cultures, which was due to the dramatic decrease of kLa in high oxygen supply culture resulted from significantly increasing apparent viscosity of the broth. The rheological properties of the three cultures all exhibited shear-thinning behavior. The oxygen uptake rate (OUR) predominately influenced by kLa was suggested to replace DO as on-line control parameter for scale-up production of DHA.

Fatty acid shifts and metabolic activity changes of Schizochytrium sp. S31 cultured on glycerol.

DHA production by Schizochytrium sp. S31 was studied in batch cultures on glycerol with stepwise dissolved oxygen strategy. Three growth stages were identified as cell growth, lipid accumulation and lipid turnover. It was revealed that fatty acid (FA) shifts during the three growth stages involved the activity changes of glycerol kinase (GK), FAD(+)-dependent glycerol-3-phosphate dehydrogenase (FAD(+)-G-3-PDH), malic enzyme (ME), ATP citrate lyase (ACL) and NAD(+)-dependent isocitrate dehydrogenase (NAD(+)-ICDH). Glycerol dissimilation in Schizochytrium sp. S31 was suggested via a phosphorylation by GK and a following oxidation by FAD(+)-G-3-PDH. Lipid accumulation of this strain was a growth-associated process, but the assimilable nitrogen depletion enhanced the accumulation of lipids. The exhaustion of glycerol induced the lipid turnover stage, where the short chain fatty acids were preferentially degraded and converted into lipid-free biomass (Xf) which was correlated to the increase of DHA content in biomass.

Improvement of docosahexaenoic acid production on glycerol by Schizochytrium sp. S31 with constantly high oxygen transfer coefficient.

Volumetric mass transfer coefficient (kLa) is a key fermentation parameter for the production of docosahexaenoic acid (DHA) from glycerol by Schizochytrium sp. S31. In order to elucidate the effects of kLa on the fermentations, both baffled and unbaffled flask cultures and fed-batch cultures were developed in present work. The results showed that high kLa could effectively increase the DHA concentration, DHA productivity and conversion yield (Yx/s, g/g). When kLa was set at 1802 ± 105 h(-1) in the fed-batch culture, DHA concentration was achieved at 28.93 g/L, DHA productivity at 301 mg/L/h and Yx/s at 0.44 ± 0.02 g/g, all of which were significantly higher than those in the previous similar studies.

[Influence of culture mode on bacterial cellulose production and its structure and property].

Acetobacter xylinum NUST4.2 has been applied in the studies to examine the production, structure and thermal property of bacterial cellulose (BC) produced in stationary culture and in the stirred tank reactor. These differences are as follows: BC yield reached 7.5 g/L in stationary culture for 6 days and its productivity was 0.052 g/L/h. BC production reached 3.13 g/L in the stirred tank reactor for 72h and its productivity was 0.043 g/L/h. SEM showed that there was almost no difference between network structure built of entangled cellulose ribbons produced in static culture and in the reactor. But the cellulose ribbons produced in static culture were a much more entangled and denser network with curved and overlapping cellulose ribbons in comparison with that one produced in the stirred tank reactor. Also the thickness of the cellulose ribbons seems to differ between the two BC samples, with the one from static culture distinguished by the slightly thinner ribbons. FT-IR revealed that there was no effect of stirring on the chemical structure of BC, but intermolecular hydrogen bond of cellulose was weakened. Furthermore, BC synthesized in static culture displayed I(alpha)-rich cellulose. XRD results indicated that no remarkable change in the cellulose crystallographic form of the BC samples. Nevertheless, BC produced in static culture was characterized by a higher crystallinity, higher I(alpha) content and higher crystalline size than cellulose that was produced in the reactor. All of these results revealed that stirring in the reactor interfere strongly in the process of nascent microfibrils crystallization, favoring the formation of smaller size microfibrils and increased I(beta), the more stable allomorph. Compared with cotton cellulose, the changes of thermal decomposition behavior in the BC samples were that BC produced in static culture displayed better thermal stability, but BC produced in the stirred reactor displayed better flame retarding.